iPad Screenshots


FM4 is a four operator FM synthesizer for iPad.

- Reached rank #1 in the app store top paid music category in 32 countries, including United States, Canada, UK, Germany, France, Brazil, Italy, Russia, Australia, and India.


- Four operators configurable in eight different routings
- Three sound engines modelled on 1980s hardware units
- Eight waveforms derived from classic FM synths
- 2x, 3x, and 4x polyphonic unison
- Tempo-syncable arpeggiator with up, down, up-down, and random patterns
- Microtuning with eight different temperaments
- Inter-App Audio
- Supports Audiobus 2
- MIDI over bluetooth
- Up to 24 voices of polyphony
- Presets can be imported/exported through iTunes

Modelled on the popular DX series from the 1980s FM4 provides the same gritty sound, with a modern interface, and without being bound by the limitations of the original units.

Every aspect of the hardware — from envelope curves to sine-table sizes and quantisation errors to digital-to-analogue converters — has been meticulously analysed, in order to recreate the raw and dirty sound of the original units.

The interface has been carefully thought-out and is simple and intuitive, yet powerful — with every parameter being available on a single page. No menus, tabs, or jumping from page to page.

FM4 is capable of producing a multitude of sounds, ranging from punchy basses, crystal-clear bells, and lush pads, to organic textures, striking drums, and piercing leads.

All product names used are trademarks of their respective owners, and reference to these here in no way constitutes an association or affiliation with Primal Audio. All trademarks are solely used to identify the products whose sound was studied during the development of FM4.

What’s New

Version 1.2.2

This app has been updated by Apple to display the Apple Watch app icon.

- Fixed bug in iOS 9 where the operator buttons would disappear.
- Minor bug corrections.

Disclaimer: The are some problems with the locations of popovers in iOS 9.0. We are waiting for Apple to look into this.

Ratings and Reviews

4.6 out of 5
19 Ratings

19 Ratings

Korg Fan ,

FM Synthesis for beginners?

This is a great app based on the TX81Z synthesizer! Despite what Primal Audio claims about the display bugs, I had no problem running it on an iPad Air 2. The presets are great and show what four operators can really do (beyond Sega Genesis sounds). If you have problems, get DXi instead. I am so happy that this app has every single parameter on a single screen!

Strizbiz ,

Great synth, 2 bad it’s not being updated

This is a great fm synth, especially if you’re just getting into fm synthesis, unfortunately it appears to be abandoned. The only thing it needs is to be an audio unit, which probably won’t happen. The landscape has changed with Auv3 support and I really use non audio unit less and less so this probably won’t remain on my iPad much longer but it was nice while it lasted

Matreve ,

Sounds amazing.

This synth sounds very good. The sounds are not digital in their character. The user interface is well thought out and straightforward. I wish the keyboard width could be changed. I also hope this app will be updated.

App Privacy

The developer, Primal Audio, has not provided details about its privacy practices and handling of data to Apple.

No Details Provided

The developer will be required to provide privacy details when they submit their next app update.


  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

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